Of the blood cells only the white blood cells, the leukocytes, have nuclei and are able to produce the many proteins found in blood plasma. One mm.sup.3 of blood contains about 6 000 to 10 000 leukocytes. A subgroup of leukocytes are the granulocytes which again are subdivided into neutrophilic polymorph-nuclear granulocytes, which account for about 95% of all granulocytes, eosinophilic granulocytes and basophilic granulocytes. In healthy adults about 10.sup.11 granulocytes are released daily from the bone marrow, but this can be increased ten fold during severe infections and inflammatory conditions. Normally the leukocytes have a transit time of about 6 hours in the circulation before entering the tissues where they perform their biological functions and are eventually sequestered. Turnover of leukocytes may vary considerably in health and disease as shown by studies using isotope labelled granulocytes as well as histological methods showing varying degrees of leukocyte infiltration in tissues. However, none of these methods is readily available for clinical studies on the turnover of leukocytes. An alternative and more readily available method may be to monitor the release of one or more characteristic leukocyte proteins during the function and/or the sequestration of the leukocytes.